Magnesium based gettering regions for gallium and nitrogen containing laser diode devices

ABSTRACT

In an example, the present invention provides a gallium and nitrogen containing laser diode device. The device has a gallium and nitrogen containing substrate material comprising a surface region, which is configured on either a non-polar ({10-10}) crystal orientation or a semi-polar ({10-10} crystal orientation configured with an offcut at an angle toward or away from the [0001] direction). The device also has a GaN region formed overlying the surface region, an active region formed overlying the surface region, and a gettering region comprising a magnesium species overlying the surface region. The device has a p-type cladding region comprising an (InAl)GaN material doped with a plurality of magnesium species formed overlying the active region.

FIELD

The present invention relates to gallium and nitrogen containing laserdiode devices. The devices include a gallium and nitrogen containingsubstrate material comprising a surface region, which is configured oneither a non-polar ({10-10}) crystal orientation or a semi-polar({10-10} crystal orientation configured with an offcut at an angletoward or away from the [0001] direction). The devices also have a GaNregion formed overlying the surface region, an active region formedoverlying the surface region, and a gettering region comprising amagnesium species overlying the surface region. The devices have ap-type cladding region comprising an (InAl)GaN material doped with aplurality of magnesium species formed overlying the active region.

BACKGROUND

The present application relates to U.S. application Ser. No. 13/019,897filed on Feb. 2, 2011, and U.S. application Ser. No. 13/328,978 filed onDec. 16, 2011, each of which is incorporated by reference in itsentirety.

The present disclosure relates generally to optical techniques. Morespecifically, the present disclosure provides methods and devices usingsemi-polar oriented gallium and nitrogen containing substrates foroptical applications.

In 1960, the laser was first demonstrated by Theodore H. Maiman atHughes Research Laboratories in Malibu. This laser utilized asolid-state flashlamp-pumped synthetic ruby crystal to produce red laserlight at 694 nm. By 1964, blue and green laser output was demonstratedby William Bridges at Hughes Aircraft utilizing a gas laser designcalled an Argon ion laser. The Ar-ion laser utilized a noble gas as theactive medium and produce laser light output in the UV, blue, and greenwavelengths including 351 nm, 454.6 nm, 457.9 nm, 465.8 nm, 476.5 nm,488.0 nm, 496.5 nm, 501.7 nm, 514.5 nm, and 528.7 nm. The Ar-ion laserhad the benefit of producing highly directional and focusable light witha narrow spectral output, but the wall plug efficiency was <0.1%, andthe size, weight, and cost of the lasers were undesirable as well.

As laser technology evolved, more efficient lamp pumped solid statelaser designs were developed for the red and infrared wavelengths, butthese technologies remained a challenge for blue and green and bluelasers. As a result, lamp pumped solid state lasers were developed inthe infrared, and the output wavelength was converted to the visibleusing specialty crystals with nonlinear optical properties. A green lamppumped solid state laser had 3 stages: electricity powers lamp, lampexcites gain crystal which lases at 1064 nm, 1064 nm goes into frequencyconversion crystal which converts to visible 532 nm. The resulting greenand blue lasers were called “lamped pumped solid state lasers withsecond harmonic generation” (LPSS with SHG) had wall plug efficiency ofabout 1%, and were more efficient than Ar-ion gas lasers, but were stilltoo inefficient, large, expensive, fragile for broad deployment outsideof specialty scientific and medical applications. Additionally, the gaincrystal used in the solid state lasers typically had energy storageproperties which made the lasers difficult to modulate at high speedswhich limited its broader deployment.

To improve the efficiency of these visible lasers, high power diode (orsemiconductor) lasers were utilized. These “diode pumped solid statelasers with SHG” (DPSS with SHG) had 3 stages: electricity powers 808 nmdiode laser, 808 nm excites gain crystal which lases at 1064 nm, 1064 nmgoes into frequency conversion crystal which converts to visible 532 nm.The DPSS laser technology extended the life and improved the wall plugefficiency of the LPSS lasers to 5% to 10%, and furthercommercialization ensue into more high end specialty industrial,medical, and scientific applications. However, the change to diodepumping increased the system cost and required precise temperaturecontrols, leaving the laser with substantial size, power consumptionwhile not addressing the energy storage properties which made the lasersdifficult to modulate at high speeds.

As high power laser diodes evolved and new specialty SHG crystals weredeveloped, it became possible to directly convert the output of theinfrared diode laser to produce blue and green laser light output. These“directly doubled diode lasers” or SHG diode lasers had 2 stages:electricity powers 1064 nm semiconductor laser, 1064 nm goes intofrequency conversion crystal, which converts to visible 532 nm greenlight. These lasers designs are meant to improve the efficiency, costand size compared to DPSS—SHG lasers, but the specialty diodes andcrystals required make this challenging today. Additionally, while thediode-SHG lasers have the benefit of being directly modulate-able, theysuffer from severe sensitivity to temperature, which limits theirapplication.

From the above, it is seen that techniques for improving optical devicesis highly desired.

SUMMARY

In an example, the present invention provides a gallium and nitrogencontaining laser diode device. The device has a gallium and nitrogencontaining substrate material comprising a surface region, which isconfigured on either a non-polar ({10-10}) crystal orientation or asemi-polar ({10-10} crystal orientation configured with an offcut at anangle toward or away from the [0001] direction). The device also has aGaN region formed overlying the surface region, an active region formedoverlying the surface region, and a gettering region comprising amagnesium species overlying the surface region. The device has a p-typecladding region comprising an (InAl)GaN material doped with a pluralityof magnesium species formed overlying the active region.

In an alternative example, the present invention provides a method ofmanufacturing a gallium and nitrogen containing laser diode device. Themethod includes providing a gallium and nitrogen containing substratematerial comprising a surface region, which is configured on either anon-polar ({10-10}) crystal orientation or a semi-polar ({10-10} crystalorientation configured with an offcut at an angle toward or away fromthe [0001] direction such as a {40-4-1} plane, a {40-41} plane, a{30-3-1} plane, a {30-31} plane, a {20-2-1} plane, a {20-21} plane, a{30-3-1} plane, a {30-32} plane, or an offcut from these planes within+/−5 degrees toward an a-plane or c-plane). The method includes forminga GaN region formed overlying the surface region, an active regionformed overlying the surface region, and a gettering region comprising amagnesium species overlying the surface region. The method includesforming a p-type cladding region comprising an (InAl)GaN material dopedwith a plurality of magnesium species formed overlying the activeregion.

In an example, the semipolar plane is selected from one of a {30-3-1}plane, a {30-31} plane, a {20-2-1} plane, a {20-21} plane, a {30-3-1}plane, a {30-32} plane, or an offcut from these planes within +/−5degrees toward an a-plane or c-plane. In an example, the device has anelectron blocking region between the gettering region and the p-typecladding region.

In an alternative example, the device has a barrier region between theactive region and the gettering region. The barrier region can compriseGaN or InGaN layers. In an example, the device has a GaN barrier regionand wherein the p-type cladding region is a GaN p-cladding regionsubstantially free from an aluminum bearing species.

In an example, the device has a separate confinement heterostructureregion between the active region and the gettering region configured toconfine an optical mode; the separate confinement heterostructurecomprised of InGaN. The separate confinement heterostructure regioncomprises an InGaN layer in an example.

In an example, the p-type cladding region comprises a plurality oflayers, the plurality of layers comprising GaN, AlGaN, and/or InAlGaNdoped with various concentrations of magnesium, which can includevarious concentrations of magnesium in the plurality of layers rangesfrom 5E17 cm⁻³ to 3E19 cm⁻³. In an example, the p-type cladding regioncomprises a single layer or comprises multiple regions. In an example,at least a portion of the p-type cladding region is epitaxially grown ata temperature above about 900° C. and the gettering region is providedat a temperature of less than about 900 degrees Celsius. In an example,at least a portion of the p-type cladding region is epitaxially grown ata temperature above about 900° C. and the gettering region is providedat a temperature of less than about 850 degrees Celsius. In an example,at least a portion of the p-type cladding region is epitaxially grown ata temperature above about 950° C. and the gettering region is providedat a temperature of less than about 850 degrees Celsius. In an example,at least a portion of the p-type cladding region is epitaxially grown ata temperature above 1000 C and the gettering region is provided at atemperature of less than about 850 degrees Celsius. In an example, thecladding region is formed at higher temperature than the getteringregion. In an example, the p-type cladding region is a GaN p-claddingdoped with a Mg concentration of less than 2E19 cm⁻³ or less than about5E18 cm⁻³.

In an example, the gettering region comprising a magnesium species dopedto increase incorporation of unintentionally incorporated magnesium froma first concentration to a second concentration. In an example, thegettering region comprises an intentionally doped region with Mg and anunintentional Mg doping region configured to incorporate any residual Mgbefore formation of the p-type region. In an example, the getteringregion comprises a thickness of 2 nm to 50 nm and/or the getteringregion comprises GaN, AlGaN, InAlGaN, or a combination thereof.

In an example, the electron blocking region comprises AlGaN or InAlGaNwith an AN mole fraction ranging from 5% to 35%. In an example, theelectron blocking region comprises AlGaN or AlInGaN, and configured witha wider band gap than a barrier region configured within a vicinity ofthe electron blocking region. In an example, the electron blockingregion is doped with a magnesium concentration between 5E18 cm⁻³ and8E19 cm⁻³. In an example, each of the electron blocking region and thep-type cladding region are epitaxially grown at a temperature aboveabout 900° C. In an example, the electron blocking region and at least aportion of the p-type cladding region are epitaxially grown at atemperature above about 900° C. and the gettering region is provided ata temperature of less than about 850 degrees Celsius. In an example, theelectron blocking region is substantially free from magnesium doping. Inan example, the electron blocking region is composed of at least one ofGaN, InAlN or AlInGaN.

In an example, the active region comprises InGaN quantum wellsconfigured to emit in the blue (430-48 nm) range or in the green (500 nmto 540 nm) range. In an example, the active region comprises a pluralityof quantum well regions. In an example, the active region comprises oneor more light emitting layers, each of the lighting emitting layersbeing configured between a pair of barrier regions, each of the lightingemitting layers having a thickness ranging from 2 to about 8 nm; andwherein each of the barrier regions has a thickness ranging from 2 to 20nm or 2 to 4 nm or 4 to 20 nm.

Embodiments provided by the present disclosure achieve these benefitsand others in the context of known process technology. However, afurther understanding of the nature and advantages of the embodimentsdisclosed herein may be realized by reference to the specification andthe attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of ideal Mg concentrationprofile near an AlGaN electron blocking layer and the impact of Mgdiffusion and the Mg-Memory effect on how Mg concentration profilesdiffer in practice from the ideal. In the ideal case (dashed horizontalline) steps in Mg concentration are sharply defined. In the case withsignificant Mg diffusion (solid line) the peak Mg concentration in theEBL is reduced and the steps in the Mg profile become graded as Mgdiffuses from the EBL into the surrounding, lower-Mg-concentrationmaterial. In the case with Mg memory-effect (dashed line) the highconcentration of Mg precursor (Cp₂Mg) used in the growth of the higherMg-concentration EBL results in residual Mg in the MOCVD chamber thatacts as an unwanted source of Mg. The unintentionally incorporated Mgresults in a tail of Mg extending up into layers grown immediately afterthe EBL at concentrations larger than those expected from Mg-diffusionalone. As time passes, and more material is grown, the source ofunintentional Mg is depleted until the background Mg concentrations areonce again below the intentional Mg concentration.

FIGS. 2A and 2B show Secondary Ion Mass Spectrometry (SIMS) profiles ofMg concentration in GaN layers grown on a (30-3-1) substrate undertypical p-type GaN growth conditions. These test structures consisted oftwo unintentionally doped (UID) GaN layers (layers 1 and 2) on eitherside of a 10 nm thick Mg-doped GaN layer; Mg precursor flow in the UIDGaN layers was zero. Mg flow in the doped GaN film was varied over anorder of magnitude, and it can be seen in FIG. 2A that at each dopinglevel a long tail of Mg is observed extending greater than 100 nm intothe otherwise un-doped layer 2. FIG. 2B shows a similar test structure,where 10 nm of Mg-doped AlGaN is clad on either side (layers 1 and 2) byUID GaN. Layer 3 is a GaN layer doped with Mg at typical concentrationsfor reference. From FIG. 1 one can see that one will not be able to growa stack of layers with arbitrary Mg concentration profile simply bymodulating the Mg precursor flow.

FIG. 3A shows a schematic of a test structure grown on a (10-10)substrate similar to those in FIG. 2B, which consist of UID GaN claddingsurrounding a Mg-doped AlGaN layer. Immediately following the growth ofthe Mg-doped AlGaN a thin (<10 nm) UID InAlGaN layer was grown. Thebaseline sample has no InAlGaN Mg-gettering layer.

FIG. 3B shows SIM profiles of the structure illustrated in FIG. 3A.

FIG. 4A shows a (30-3-1) oriented four-layer test structure comprised ofAlGaN layers separated by UID GaN grown under typical p-GaN conditions.Between the UID p-GaN and the AlGaN are thin layers of GaN grown atlower temperatures than one would typically grow high quality Mg-dopedGaN.

FIG. 4B shows SIM profiles of the structure illustrated in FIG. 4A.

FIG. 5 shows a schematic and definitions used for example embodiments.

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS

Light emitting diodes and laser diodes are derived from semiconductorp-n junction diodes. These devices a comprised of various layers ofsemiconducting material doped with impurities such that one side of thedevice is “n-type” (i.e. electrons are the majority carrier species) andthe other side is “p-type” (i.e. holes are the majority carrierspecies). In the III-V nitrides, p-type conductivity is predominantlyachieved by doping the (InAl)GaN layer with magnesium, which is arelatively deep acceptor in the III-nitrides. As opposed to a dopantspecies like Si, where the majority of the dopant atoms contributeelectrons to conduction, the depth of the Mg acceptor state in theIII-Nitride bandgap results in very few of the Mg atoms contributing toconduction. This combined with the volatility of Mg result in the needfor the introduction of relatively large concentrations of Mg-bearingmetal-organic precursors (typically Cp₂Mg) into the MOCVD chamber duringgrowth of Mg-doped layers. This is unfortunate, as Cp₂Mg is widely knownto exhibit the so-called “memory” effect, whereby Mg metal-organicprecursors remain in the chamber for some time after the intentionalintroduction of the precursor gas is stopped resulting in theunintentional incorporation of Mg into the subsequently grown layers. Asecond consequence of the high flows of Mg is the accumulation ofunincorporated Mg on the growing surface of the epitaxial film. Thisexcess of Mg will remain on the surface after the Mg precursor flow ishalted resulting in the unintentional incorporation of Mg into thesubsequently grown layers.

In laser diodes, this “memory effect” of residual Mg in the chamber andon the sample surface is particularly damaging to performance. Mg-dopedGaN is highly absorbing, and absorption of light from the lasing opticalmode is a significant source of loss in III-Nitride laser diodes.Ideally, one would design the Mg concentration profile such that layerssuch as the electron blocking layer (typically composed of AlGaN) aredoped sufficiently with Mg to ensure that the position of the depletionregion and injection efficiency of holes and electrons is optimal, butat the same time reduce to a minimum the amount of Mg in layers that donot significantly influence injection efficiency but which do interactwith the optical mode. The Mg memory effect can potentially set a lowerlimit for how low the Mg concentration can be in a given layer based onthe dose of Mg precursor introduced into the chamber in previous layers.

FIG. 1 shows a schematic representation of the expected Mg concentrationprofile near an AlGaN EBL for the ideal case as well as for cases wherethe Mg memory-effect and Mg diffusion at growth temperature arenon-negligible. Mg memory-effect results in an asymmetrical ‘tail’ of Mgextending away from the EBL-where Mg precursor flows are typicallyhighest-into the subsequently grown layers. An example of this type ofMg concentration profile can be observed in FIG. 2A, which showsSecondary Ion Mass Spectrometry (SIMS) profiles of Mg concentration inGaN layers grown under typical p-type GaN growth conditions. These teststructures consisted of two unintentionally doped (UID) GaN layers(layers 1 and 2) on either side of a 10 nm thick Mg-doped GaN layer; Mgprecursor flow in the UID GaN layers was zero. Mg flow in the doped GaNfilm was varied over an order of magnitude, and it can be seen that ateach Cp₂Mg doping level a long tail of Mg is observed extending greaterthan 100 nm into the otherwise un-doped layer 2. FIG. 2B shows a similartest structure, where 10 nm of Mg-doped AlGaN is clad on either side(layers 1 and 2) by UID GaN. Layer 3 is a GaN layer doped with Mg attypical concentrations for reference. From FIG. 1 one can see that onewill not be able to grow a stack of layers with arbitrary Mgconcentration profile simply by modulating the Mg precursor flow.

It is, however, possible to change the rate of Mg incorporation byadjusting layer composition and growth conditions such that the rate ofMg incorporation is increased, thereby incorporating the residual Mginto a thinner layer resulting in a higher peak concentration. FIG. 3Ashows a set of test structures similar to those in FIGS. 2A and 2B. Thetest structures shown in FIG. 3A consist of UID GaN cladding surroundinga Mg-doped AlGaN layer. Immediately following the growth of the Mg-dopedAlGaN a thin (<10 nm) UID InAlGaN layer was grown at differenttemperatures from 800° C. to 950° C. As shown in FIG. 3B it can be seenthat this layer results in two changes to the Mg-profile. The first isthat this layer getters Mg from the MOCVD chamber and the samplesurface, leading to a significantly higher peak Mg concentration.Secondly, this preferential incorporation of Mg results in a sharperdecrease in the Mg concentration in the subsequently grown UID GaNlayer. Due to the relatively poor depth resolution of SIMS andtransients in Mg incorporation the Mg concentrations in the EBL andgettering layer are convolved into a single peak.

In order to obtain arbitrary doping profiles, Mg can be added to thegetter layer directly. FIG. 4B shows SIMS concentration profiles for afour-layer test structure as shown in FIG. 4A consisting of AlGaN layersseparated by UID GaN grown under typical p-GaN conditions. Between theUID p-GaN and the AlGaN are thin layers of GaN grown at lowertemperatures than one would typically grow high quality Mg-doped GaN.The layer sets marked ‘A’ and ‘B’ contain AlGaN doped with a low flow ofMg, and the low temperature GaN layers were grown with differenttransitions between the AlGaN and LT GaN layers. Here thelow-temperature GaN layers result in a spike in the Mg-concentrationmeasured by SIMS, but are not able to incorporate all of the residual Mgresulting in significant Mg concentrations in the subsequently grown UIDGaN. Layers ‘C’ and ‘D’ contain UID AlGaN, and the low-temperature GaNlayers are doped with a small flow of Mg. This results in peak Mgconcentrations similar to those in ‘A’ and ‘B’ while retaining the sharpturn-on and turn-off of the Mg concentration profile.

This Mg memory effect has been observed in GaN films of variousorientations including non-polar, semi-polar and c-plane. We haveobserved the effectiveness of getter layers in both m-plane as well as(30-3-1) oriented films.

An AlInGaN laser diode with non-polar ({10-10}) or semi-polar ({10-10}offcut at large angles toward or away from the [0001] direction such asa {40-4-1} plane, a {-40-41}, a {30-3-1} plane, a {30-31} plane, a{20-2-1} plane, a {20-21} plane, a {30-3-1} plane, a {30-32} plane, oran offcut from these planes within +/−5 degrees toward an a-plane orc-plane.) crystal orientation where there is an epitaxial layer grownbetween any of the various Mg-doped layers where (A) the growthconditions or composition of the layer are different from adjacentlayers and (B) the layer composition and/or growth conditions are chosento preferentially incorporate (i.e. getter) residual Mg resulting fromprevious Mg-doped layer growth that otherwise would be incorporated insubsequently grown layers. This invention is associated in particularwith getter layers dispositioned between highly Mg-doped layers grownnear the light emitting layer(s) and subsequently grown layerscomprising the p-cladding.

Certain embodiments of the present disclosure are provided in thefollowing. FIG. 5 shows the structure of the devices covered in theseexample embodiments and description of individual layers.

Embodiment 1: a non-polar or semi-polar, blue or green LD consisting ofone or more light emitting layers with an AlGaN EBL, a GaN upper barrierand GaN p-cladding. The EBL is doped uniformly with a Mg concentrationbetween 5E18 cm⁻³ and 5E19 cm⁻³. The GaN p-cladding is doped uniformlywith a Mg concentration of less than 2E18 cm⁻³. The EBL and pGaN areboth grown at a temperature above 900° C. After EBL growth is complete,flow of the Mg precursor to the reactor growth chamber is interruptedand the substrate temperature is decreased to 800 degrees Celsius and 10nm of nominally undoped GaN is grown in order to getter residual Mg. Thesubstrate temperature is then increased to the p-cladding growthtemperature while conditions are ramped to the p-cladding growthconditions. Once the reactor conditions are stable the Mg precursor isreintroduced to the reactor and growth of the Mg-doped p-cladding layersis commenced.

Embodiment 2: A device similar to that of embodiment 1 where the Mggetter layer is grown with a small flow of Mg precursor into the growthchamber. Mg flow during the getter layer growth is chosen such that thepeak Mg concentration in the getter layer is higher than what would beachieved using a not-intentionally doped getter layer while keeping theMg flow low enough that there is not a net increase in residual Mg.

Embodiment 3: a device similar to that of embodiment 1 where the EBL isgrown without Mg doping and the getter layer is intentionally doped withMg to a concentration high enough to ensure good electrical performanceof the device.

Embodiment 4: a device similar to that of embodiments 2 or 3 where thegettering layer consists of two parts. The first part is grownintentionally doped with Mg (to produce an adequate peak Mgconcentration) and the second part is grown without intentional Mgdoping (to quickly incorporate any residual Mg before the p-cladding isgrown).

Embodiment 4b: a device similar to that of 2 or 3 where the getteringlayer consists of a multiplicity of intentionally doped andnon-intentionally doped layers.

Embodiment 5: a device similar to that of embodiments 2, 3, 4 or 4bwhere the EBL is composed of some composition of GaN, InAlN or AlInGaN.

Embodiment 6: a device similar to that of 2, 3, 4, 4b and 5 where thegetter layer has a composition similar to that of the EBL.

Embodiment 7: a device similar to that of 3, 4 or 4b where the EBL isremoved from the structure and the getter layer contains at least onelayer that is intentionally doped. The getter layer can be anycomposition of AlInGaN.

Embodiment 8: a device similar to those of 1, 2, 3, 4, 4b, 5, 6 or 7where the p-cladding consists of one or more low index layers such asAlGaN or AlInGaN.

Embodiment 9: a device similar to 1-8 which contains an InGaN layerbetween the getter layer and the p-cladding to help shape the opticalmode.

In an example, the present invention provides the following method, asoutlined in the following.

Provide a gallium and nitrogen containing substrate material comprisinga surface region, which is configured on either a non-polar ({10-10})crystal orientation or a semi-polar ({10-10} crystal orientationconfigured with an offcut at an angle toward or away from the [0001]direction such as {40-4-1}, {40-41}, {30-3-1}, {30-31}, {20-2-1},{20-21}, {30-3-1}, {30-32}, or an offcut from these planes within +/−5degrees toward an a-plane or c-plane);

Form a GaN region formed overlying the surface region;

Form an active region formed overlying the surface region;

Form a gettering region comprising a magnesium species overlying thesurface region;

Form a p-type cladding region comprising an (InAl)GaN material dopedwith a plurality of magnesium species formed overlying the activeregion; and

Perform other steps, as desired.

Further details of the present method can include certain processrecipes as described in more detail below.

In an example, the optical device includes a gallium nitride substratemember having a semipolar crystalline surface region characterized by anorientation of about 9 degrees to about 12.5 degrees toward (000-1) fromthe m-plane.). In a specific embodiment, the gallium nitride substratemember is a bulk GaN substrate characterized by having a semipolarcrystalline surface region, but can be others. In a specific embodiment,the bulk GaN substrate has a surface dislocation density below 10⁵ cm⁻²or 10⁵ to 10⁷ cm⁻². It should be noted that homoepitaxial growth on bulkGaN is generally better than hetero-epitaxy growth. The nitride crystalor wafer may comprise Al_(x)In_(y)Ga_(1-x-y)N, where 0≦x, y, x+y≦1. Inone specific embodiment, the nitride crystal comprises GaN. In one ormore embodiments, the GaN substrate has threading dislocations, at aconcentration between about 10⁵ cm⁻² and about 10⁸ cm², in a directionthat is substantially orthogonal or oblique with respect to the surface.As a consequence of the orthogonal or oblique orientation of thedislocations, the surface dislocation density is below about 10⁵ cm⁻² orothers such as those ranging from about 10⁵ cm⁻² to 10⁸ cm⁻².

In a specific embodiment, the device has a laser stripe region formedoverlying a portion of the semipolar crystalline orientation surfaceregion. In a specific embodiment, the laser stripe region ischaracterized by a cavity orientation is substantially parallel to theprojection of the c-direction. In a specific embodiment, the laserstripe region has a first end and a second end. In a preferredembodiment, the device has a first facet provided on the first end ofthe laser stripe region and a second facet provided on the second end ofthe laser stripe region. In one or more embodiments, the first facet issubstantially parallel with the second facet. Mirror surfaces are formedon each of the surfaces. The first facet comprises a first mirrorsurface. In a preferred embodiment, the first mirror surface is providedby an etching process. The etching process can use any suitabletechniques, such as a chemical etching process using a CAIBE etchingprocessor combinations. In a specific embodiment, the first mirrorsurface comprises a reflective coating. In a specific embodiment,deposition of the reflective coating occurs using, for example, e-beamevaporation, thermal evaporation, RF sputtering, DC sputtering, ECRsputtering, ion beam deposition, Ion Assisted Deposition, reactive ionplating, any combinations, and the like. In still other embodiments, thepresent method may provide surface passivation to the exposed surfaceprior to coating. The reflective coating is selected from silicondioxide, hafnia, and titania, tantalum pentoxide, zirconia, includingcombinations, and the like. Preferably, the reflective coating is highlyreflective and includes a coating of silicon dioxide and tantalumpentoxide, which has been deposited using electron beam deposition.Depending upon the embodiment, the first mirror surface can alsocomprise an anti-reflective coating. Additionally, the facets can beetched or a combination of them.

Also in a preferred embodiment, the second facet comprises a secondmirror surface. The second mirror surface is provided by an etchingtechniques using etching technologies such as reactive ion etching(RIE), inductively coupled plasma etching (ICP), or chemical assistedion beam etching (CAIBE), or other method. In an example, (CAIBE),(ICP), or (RIE) can result in smooth and vertical etched sidewallregions, which could serve as facets in etched facet laser diodes. Inthe etched facet process a masking layer is deposited and patterned onthe surface of the wafer. The etch mask layer could be comprised ofdielectrics such as silicon dioxide (SiO₂), silicon nitride(Si_(x)N_(y)), a combination thereof or other dielectric materials.Further, the mask layer could be comprised of metal layers such as Ni orCr, but could be comprised of metal combination stacks or stackscomprising metal and dielectrics. In another approach, photoresist maskscan be used either alone or in combination with dielectrics and/ormetals. The etch mask layer is patterned using conventionalphotolithography and etch steps. The alignment lithography could beperformed with a contact aligner or stepper aligner. Suchlithographically defined mirrors provide a high level of control to thedesign engineer. After patterning of the photoresist mask on top of theetch mask is complete, the patterns in then transferred to the etch maskusing a wet etch or dry etch technique. Finally, the facet pattern isthen etched into the wafer using a dry etching technique selected fromCAIBE, ICP, RIE and/or other techniques. The etched facet surfaces mustbe highly vertical of between about 87 and 93 degrees or between about89 and 91 degrees from the surface plane of the wafer. The etched facetsurface region must be very smooth with root mean square roughnessvalues of less than 50 nm, 20 nm, 5 nm, or 1 nm. Lastly, the etchedshould be substantially free from damage, which could act asnon-radiative recombination centers and hence reduce the COMD threshold.In an example, CAIBE is provides very smooth and low damage sidewallsdue to the chemical nature of the etch, while it can provide highlyvertical etches due to the ability to tilt the wafer stage to compensatefor any angle in etch in an example.

In a specific embodiment, the second mirror surface comprises areflective coating, such as silicon dioxide, hafnia, titania, tantalumpentoxide, zirconia, combinations, and the like. In a specificembodiment, the second mirror surface comprises an anti-reflectivecoating, such alumina or aluminum oxide. In a specific embodiment, thecoating can be formed using electron beam deposition, thermalevaporation, RF sputtering, DC sputtering, ECR sputtering, ion beamdeposition, ion assisted deposition, reactive ion plating, anycombinations, and the like. In still other embodiments, the presentmethod may provide surface passivation to the exposed surface prior tocoating.

In a specific embodiment, the laser stripe has a length and width. Thelength ranges from about 200 microns to about 3000 microns. The stripealso has a width ranging from about 0.5 microns to about 50 microns, butcan be other dimensions. In a specific embodiment, the stripe can alsobe about 6 to 25 microns wide for a high power multi-lateral-mode deviceor 1 to 2 microns for a single lateral mode laser device. In a specificembodiment, the width is substantially constant in dimension, althoughthere may be slight variations. The width and length are often formedusing a masking and etching process, which are commonly used in the art.Further details of the present device can be found throughout thepresent specification and more particularly below.

In a specific embodiment, the device is also characterized by aspontaneously emitted light that is polarized in substantiallyperpendicular to the projection of the c-direction (in the a-direction).That is, the device performs as a laser or the like. In a preferredembodiment, the spontaneously emitted light is characterized by apolarization ratio of greater than 0.2 to about 1 perpendicular to thec-direction. In a preferred embodiment, the spontaneously emitted lightcharacterized by a wavelength ranging from about 400 nanometers to yielda violet emission, a blue emission, a green emission, and others. In oneor more embodiments, the light can be emissions ranging from violet 395to 420 nanometers; blue 430 to 470 nm; green 500 to 540 nm; and others,which may slightly vary depending upon the application. In a preferredembodiment, the spontaneously emitted light is highly polarized and ischaracterized by a polarization ratio of greater than 0.4. In a specificembodiment, the emitted light is characterized by a polarization ratiothat is desirable. Further details of the laser device can be foundthroughout the present specification and more particularly below.

In an example, a waveguide design has a nonpolar or a semipolar laserdiode that contains cladding regions that are substantially free fromaluminum. Such laser diode designs can enable high COMD levels withoutthe need for highly-specialized and costly mirror coating techniquessuch as electron cyclotron resonance (ECR). As shown in an example, thelaser device includes gallium nitride substrate, which has an underlyingn-type metal back contact region. In a specific embodiment, the metalback contact region is made of a suitable material such as those notedbelow and others. Further details of the contact region can be foundthroughout the present specification and more particularly below.

In a specific embodiment, the device also has an overlying n-typegallium nitride layer, an active region, and an overlying p-type galliumnitride layer structured as a laser stripe region. Additionally, thedevice also includes an n-side separate confinement heterostructure(SCH), p-side guiding layer or SCH, p-AlGaN EBL, among other features.In a specific embodiment, the device also has a p++ type gallium nitridematerial to form a contact region. In a specific embodiment, the p++type contact region has a suitable thickness and may range from about 10nm 50 nm, or other thicknesses. In a specific embodiment, the dopinglevel can be higher than the p-type cladding region and/or bulk region.In a specific embodiment, the p++ type region has doping concentrationranging from about 10E19 to 10E21 Mg/centimeter³, and others. The p++type region preferably causes tunneling between the semiconductor regionand overlying metal contact region. In a specific embodiment, each ofthese regions is formed using at least an epitaxial deposition techniqueof metal organic chemical vapor deposition (MOCVD), molecular beamepitaxy (MBE), or other epitaxial growth techniques suitable for GaNgrowth. In a specific embodiment, the epitaxial layer is a high qualityepitaxial layer overlying the n-type gallium nitride layer. In someembodiments the high quality layer is doped, for example, with Si or Oto form n-type material, with a dopant concentration between about 10¹⁶cm⁻³ and 10²⁰ cm⁻³.

In a specific embodiment, an n-type Al_(u)In_(v)Ga_(1-u-v)N layer, where0≦u, v, u+v≦1, is deposited on the substrate. In a specific embodiment,the carrier concentration may lie in the range between about 10¹⁶ cm⁻³and 10²⁰ cm⁻³. The deposition may be performed using metal organicchemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).

As an example, the bulk GaN substrate is placed on a susceptor in anMOCVD reactor. After closing, evacuating, and back-filling the reactor(or using a load lock configuration) to atmospheric pressure, thesusceptor is heated to a temperature between about 900 to about 1200degrees Celsius in the presence of a nitrogen-containing gas. As anexample, the carrier can be hydrogen or nitrogen or others. In onespecific embodiment, the susceptor is heated to approximately 1100degrees Celsius under flowing ammonia. A flow of a gallium-containingmetalorganic precursor, such as trimethylgallium (TMG) ortriethylgallium (TEG) is initiated, in a carrier gas, at a total ratebetween approximately 1 and 50 standard cubic centimeters per minute(sccm). The carrier gas may comprise hydrogen, helium, nitrogen, orargon. The ratio of the flow rate of the group V precursor (e.g.,ammonia) to that of the group III precursor (trimethylgallium,triethylgallium, trimethylindium, trimethylaluminum) during growth isbetween about 2000 and about 12000. A flow of disilane in a carrier gas,with a total flow rate of between about 0.1 sccm and 10 sccm isinitiated.

In a specific embodiment, the laser stripe region is made of the p-typegallium nitride layer. In a specific embodiment, the laser stripe isprovided by an etching process selected from dry etching or wet etching.In a preferred embodiment, the etching process is dry, but can beothers. As an example, the dry etching process is an inductively coupledplasma process using chlorine bearing species or a reactive ion etchingprocess using similar chemistries or combination of ICP and RIE, amongother techniques. Again as an example, the chlorine bearing species arecommonly derived from chlorine gas or the like. The device also has anoverlying dielectric region, which exposes contact region, which ispreferably a p++ gallium nitride region. In a specific embodiment, thedielectric region is an oxide such as silicon dioxide or siliconnitride, but can be others, such as those described in more detailthroughout the present specification and more particularly below. Thecontact region is coupled to an overlying metal layer. The overlyingmetal layer is a multilayered structure containing gold and platinum(Ni/Au), but can be others such as gold and palladium (Pd/Au) or goldand nickel (Ni/Au). In an alternative embodiment, the metal layercomprises Ni/Au formed using suitable techniques. In a specificembodiment, the Ni/Au is formed via electron-beam deposition,sputtering, or any like techniques. The thickness includes nickelmaterial ranging in thickness from about 50 to about 100 nm and goldmaterial ranging in thickness from about 100 Angstroms to about 1-3microns, and others.

In a preferred embodiment, the dielectric region can be made using asuitable technique. As an example, the technique may include reactivelysputter of SiO₂ using an undoped polysilicon target (99.999% purity)with O2 and Ar. In a specific embodiment, the technique uses RFmagnetron sputter cathodes configured for static deposition; sputtertarget; throw distance; pressure: 1-5 mT or about 2.5 mT, power: 300 to400 W; flows: 2-3.-9 sccm O₂, 20-50 sccm, Ar, deposition thickness:1000-2500 A, and may include other variations. In a specific embodiment,deposition may occur using non-absorbing, nonconductive films, e.g.,Al₂O₃, Ta₂O₅, SiO₂, Ta₂O₅, ZrO₂, TiO₂, HfO₂, NbO₂. Depending upon theembodiment, the dielectric region may be thinner, thicker, or the like.In other embodiments, the dielectric region can also include multilayercoatings, e.g., 1000 Å of SiO₂ capped with 500 Å of Al₂O₃. Depositiontechniques can include, among others, ebeam evaporation, thermalevaporation, RF Sputter, DC Sputter, ECR Sputter, Ion Beam Deposition,Ion Assisted Deposition, reactive ion plating, combinations, and thelike.

In a specific embodiment, the laser device has active region. The activeregion can include one to twenty quantum well regions according to oneor more embodiments. As an example following deposition of the n-typeAl_(u)In_(v)Ga_(1-u-v)N layer for a predetermined period of time, so asto achieve a predetermined thickness, an active layer is deposited. Theactive layer may comprise a single quantum well or a multiple quantumwell, with 1 to 20 quantum wells. Preferably, the active layer mayinclude about 3-7 quantum wells or more preferably 4-6 quantum wells orothers. The quantum wells may comprise InGaN wells and GaN barrierlayers. In other embodiments, the well layers and barrier layerscomprise Al_(w)In_(x)Ga_(1-w-x)N and Al_(y)In_(z)Ga_(1-y-z)N,respectively, where 0≦w, x, y, z, w+x, y+z≦1, where w<u, y and/or x>v, zso that the bandgap of the well layer(s) is less than that of thebarrier layer(s) and the n-type layer. The well layers and barrierlayers may each have a thickness between about 1 nm and about 30 nm. Ina preferred embodiment, each of the thicknesses is preferably 3-8 nm. Ina specific embodiment, each well region may have a thickness of about 5nm to 7 nm and each barrier region may have a thickness of about 2 nm toabout 5 nm, among others. In another embodiment, the active layercomprises a double heterostructure, with an InGaN orAl_(w)In_(x)Ga_(1-w-x)N layer about 10 nm to 100 nm thick surrounded byGaN or Al_(y)In_(z)Ga_(1-y-z)N layers, where w<u, y and/or x>v, z. Thecomposition and structure of the active layer are chosen to providelight emission at a preselected wavelength. The active layer may be leftundoped (or unintentionally doped) or may be doped n-type or p-type.

In a specific embodiment, the active region can also include an electronblocking region, and a separate confinement heterostructure. In aspecific embodiment, the separate confinement heterostructure (SCH) caninclude AlInGaN or preferably InGaN, but can be other materials. The SCHis generally comprised of material with an intermediate index betweenthe cladding layers and the active layers to improve confinement of theoptical mode within the active region of the laser device according to aspecific embodiment. In one or more embodiments, the SCH layers have adesirable thickness, impurity, and configuration above and below theactive region to confine the optical mode. Depending upon theembodiment, the upper and lower SCH can be configured differently or thesame. The electron blocking region can be on either side or both sidesof the SCH positioned above the active region according to a specificembodiment. In a preferred embodiment, the SCH can range from about 100nm to about 1500 nm, and preferably about 40 nm to 100 nm for the lowerSCH region. In the upper SCH region, the thickness ranges from about 20nm to 50 nm in a specific embodiment. As noted, the SCH is preferablyInGaN having about 2% to about 5% indium or 5% to about 10% by atomicpercent according to a specific embodiment.

In some embodiments, an electron blocking layer is preferably deposited.In a specific embodiment, the electron blocking layer comprises agallium and nitrogen containing material including magnesium 10E16 cm⁻³to about 10E22 cm⁻³. The electron-blocking layer may compriseAl_(s)In_(t)Ga_(1-s-t)N, where 0≦s, t, s+t≦1, with a higher bandgap thanthe active layer, and may be doped p-type. In one specific embodiment,the electron blocking layer comprises

AlGaN with an Al composition ranging from 5 to 20%. In anotherembodiment, the electron blocking layer may not contain Al. In anotherembodiment, the electron blocking layer comprises an AlGaN/GaNsuper-lattice structure, comprising alternating layers of AlGaN and GaN,each with a thickness between about 0.2 nm and about 5 nm.

As noted, the p-type gallium nitride structure, which can be a p-typedoped Al_(q)In_(r)Ga_(1-q-r)N, where 0≦q, r, q+r≦1, layer is depositedabove the active layer. The p-type layer may be doped with Mg, to alevel between about 10¹⁶ cm⁻³ and 10²² cm⁻³, and may have a thicknessbetween about 5 nm and about 1000 nm. The outermost 1 nm to 50 nm of thep-type layer may be doped more heavily than the rest of the layer, so asto enable an improved electrical contact. In a specific embodiment, thelaser stripe is provided by an etching process selected from dry etchingor wet etching. In a preferred embodiment, the etching process is dry,but can be others. The device also has an overlying dielectric region,which exposes contact region. In a specific embodiment, the dielectricregion is an oxide such as silicon dioxide, but can be others.

In a specific embodiment, the metal contact is made of suitablematerial. The reflective electrical contact may comprise at least one ofsilver, gold, aluminum, nickel, platinum, rhodium, palladium, chromium,or the like. The electrical contact may be deposited by thermalevaporation, electron beam evaporation, electroplating, sputtering, oranother suitable technique. In a preferred embodiment, the electricalcontact serves as a p-type electrode for the optical device. In anotherembodiment, the electrical contact serves as an n-type electrode for theoptical device.

In a specific embodiment, a ridge waveguide is fabricated using acertain deposition, masking, and etching processes. In a specificembodiment, the mask is comprised of photoresist (PR) or dielectric orany combination of both and/or different types of them. The ridge maskis 1 to 2.5 microns wide for single lateral mode applications or 2.5 to30 um wide for multimode applications. The ridge waveguide is etched byion-coupled plasma (ICP), reactive ion etching (RIE), chemical assistedion beam (CAIBE) etched, or other method. The etched surface is 20-250nm above the active region. A dielectric passivation layer is thenblanket deposited by any number of commonly used methods in the art,such as sputter, e-beam, PECVD, or other methods. This passivation layercan include SiO2, Si3N4, Ta2O5, or others. The thickness of this layeris 80-400 nm thick. An ultrasonic process is used to remove the etchmask which is covered with the dielectric. This exposes the p-GaNcontact layer. P-contact metal is deposited by e-beam, sputter, or otherdeposition technique using a PR mask to define the 2D geometry. Thecontact layer can be Ni/Au but others can be Pt/Au or Pd/Au. Furtherdetails of the present method and resulting structure can be foundthroughout the present specification and more particularly below.Further details of the facets can be found throughout the presentspecification and more particularly below.

In one or more preferred embodiments, the present invention provides alaser structure without an aluminum bearing cladding region. In aspecific embodiment, the laser device comprises a multi-quantum wellactive region having thin barrier layers. In one or more embodiments,the active region comprises three or more quantum well structures.Between each of the quantum well structures comprises a thin barrierlayer, e.g., 7 nm and less, 6 nm and less, 5 nm and less, 4 nm and less,3 nm and less, 2 nm and less. In a preferred embodiment, the combinationof thin barrier layers configured in the multi-quantum well structuresenables a low voltage (e.g., 6 volts and less) laser diode free from useof aluminum bearing cladding regions.

In a specific embodiment, the present invention provides an opticaldevice. The optical device has a gallium and nitrogen containingsubstrate including a (30-3-1) or offcut crystalline surface regionorientation, which may be off-cut. The device preferably has an n-typecladding material overlying the n-type gallium and nitrogen containingmaterial according to a specific embodiment. The n-type claddingmaterial is substantially free from an aluminum bearing materialaccording to a specific embodiment. The device also has an active regioncomprising at least three quantum wells. Each of the quantum wells has athickness of 3.0 nm and greater or 5.5 nm and greater, and one or morebarrier layers. Each of the barrier layers has a thickness ranging fromabout 2 nm to about 5 nm or about 5 nm to about 9 nm and is configuredbetween a pair of quantum wells according to a specific embodiment. Atleast one or each of the barrier layers has a thickness ranging fromabout 2 nm to about nm and is configured between a pair of quantum wellsor adjacent to a quantum well according to a specific embodiment. Atleast one or each of the barrier layers has a thickness ranging fromabout 4 nm to about 6.5 nm and is configured between a pair of quantumwells or adjacent to a quantum well according to a specific embodiment.Preferably, the device has a p-type cladding material overlying theactive region. Preferably, the p-type cladding material is substantiallyfree from an aluminum bearing material according to a specificembodiment. In a preferred embodiment, the active region is configuredoperably for a forward voltage of less than about 6V or less than about5V for the device for an output power of 60 mW or 100 mW and greater.

In yet an alternative embodiment, the present invention provides anoptical device. The device has a gallium and nitrogen containingsubstrate including a (30-3-1) or offcut crystalline surface regionorientation. The device also has an n-type cladding material overlyingthe n-type gallium and nitrogen containing material. The n-type claddingmaterial is substantially free from an aluminum bearing material. Thedevice further has an active region comprising at least three quantumwells. Each of the quantum wells has a thickness of 3.5 nm and greateror 5 nm and greater and one or more barrier layers according to aspecific embodiment. Each of the barrier layers has a thickness rangingfrom about 2 nm to about 4 nm or about 4 nm to about 8 nm according to aspecific embodiment. Each of the barrier layers is configured between apair of quantum wells according to one or more embodiments. At least oneor each of the barrier layers has a thickness ranging from about 2 nm toabout 5 nm and is configured between a pair of quantum wells or adjacentto a quantum well according to a specific embodiment. At least one oreach of the barrier layers has a thickness ranging from about 4 nm toabout 8 nm and is configured between a pair of quantum wells or adjacentto a quantum well according to a specific embodiment. The device alsohas a p-type cladding material overlying the active region. The p-typecladding material is substantially free from an aluminum bearingmaterial according to a preferred embodiment. The device optionally hasa p-type material overlying the p-type cladding material.

In other embodiments, the invention provides yet an alternative opticaldevice, which has a gallium and nitrogen containing substrate includinga (30-3-1) or offcut crystalline surface region orientation. An n-typecladding material is overlying the n-type gallium and nitrogencontaining material. Preferably, the n-type cladding material issubstantially free from an aluminum bearing material. The device has anactive region comprising at least three quantum wells, each of which hasa thickness of 4 nm and greater. The device has one or more barrierlayers, each of which has an n-type impurity characteristic and athickness ranging from about 2 nm to about 4 nm or about 4 nm to about 8nm in one or more alternative embodiments. Preferably, each of thebarrier layers is configured between a pair of quantum wells accordingto a specific embodiment. The device also has a p-type cladding materialoverlying the active region according to a specific embodiment. Thep-type cladding material is substantially free from an aluminum bearingmaterial according to a specific embodiment. The device also has ap-type material overlying the p-type cladding material.

In other embodiments, the invention provides a method of fabricating anoptical device, which has a gallium and nitrogen containing substrateincluding a (30-3-1) or offcut crystalline surface region orientation.An n-type cladding material is overlying the n-type gallium and nitrogencontaining material. Preferably, the n-type cladding material issubstantially free from an aluminum bearing material. The methodincludes forming an active region comprising at least three quantumwells, each of which has a thickness of 3.5 nm and greater. The devicehas one or more barrier layers, each of which has an n-type impuritycharacteristic and a thickness ranging from about 2 nm to about 4 nm orabout 4 nm to about 8 nm in one or more alternative embodiments.Preferably, each of the barrier layers is configured between a pair ofquantum wells according to a specific embodiment. The method alsoincludes forming a p-type cladding material overlying the active regionaccording to a specific embodiment. The p-type cladding material issubstantially free from an aluminum bearing material according to aspecific embodiment. The method also includes forming a p-type materialoverlying the p-type cladding material.

In a specific embodiment, the present invention provides an opticaldevice, such as a laser diode. The device has a gallium and nitrogencontaining substrate including a (30-3-1) or offcut crystalline surfaceregion orientation, which may be off-cut according to one or moreembodiments. The device has an n-type cladding material overlying then-type gallium and nitrogen containing material. In a preferredembodiment, the n-type cladding material is substantially free from analuminum bearing material. The device also has an active regioncomprising at least three quantum wells. In a specific embodiment, eachof the quantum wells has a thickness of 3.5 nm and greater and one ormore barrier layers according to a specific embodiment. Each of thebarrier layers has a p-type characteristic and a thickness ranging fromabout 2 nm to about 3.5 nm in a specific embodiment. Each of the barrierlayers has a p-type characteristic and a thickness ranging from about3.5 nm to about 7 nm in an alternative specific embodiment. In apreferred embodiment, each of the barrier layers is configured between apair of quantum wells. The device also has a p-type cladding materialoverlying the active region. Preferably, the p-type cladding material issubstantially free from an aluminum bearing material. And overlyingp-type material is included. In a preferred embodiment, the activeregion is configured for a forward voltage of less than about 6V or lessthan about 7V for the device for an output power of 60 mW and greater.In other embodiments for nonpolar m-plane devices or semipolar (30-3-1)planes, operable in the blue (430-475 nm) and green (505-530 nm), thepresent method and structure include five (5) or more thick QWs ofgreater than 4 or 5 nm in thickness and thin barriers that are 2 nm to 4nm in thickness.

In one or more embodiments, the present invention includes a laser diodesubstantially free from an aluminum containing cladding region. To formthe laser diode without an aluminum containing cladding region, thepresent laser diode includes three or more quantum wells to provideenough confinement of the optical mode for sufficient gain to reachlasing. However, when the number of quantum wells increases in theactive region, the forward voltage of the diode can increase, as atradeoff. We have determined that the forward voltage of the diode canbe reduced in multi-quantum well active regions by way of the use ofthin barriers on the order of 3-4 nm, which are much thinner thanconventional lasers such as those in Yoshizumi et al., “Continuous-Waveoperation of 520 nm Green InGaN-Based Laser Diodes on Semi-Polar {20-21}GaN Substrates,” Applied Physics Express 2 (2009) 092101. We have alsodetermined that the forward voltage can be reduced in multi-quantum wellactive regions by adding p or n-type dopant species to the active regionaccording to one or more other embodiments. Although any one orcombination of these approached can be used, we believe it would bepreferable to use the thin barrier approach to avoid adding impuritiesto the active region. The impurities may change optical losses and alterthe electrical junction placement according to one or more embodiments.Accordingly, the present invention provides a laser device and methodthat is free from aluminum-containing cladding regions with low voltageon (30-3-1) or offcut substrates.

Moreover, the present invention provides an optical device that issubstantially free from aluminum bearing cladding materials. The devicehas a gallium and nitrogen containing substrate member having a (30-3-1)or offcut crystalline surface region. The device has an n-type galliumand nitrogen containing cladding material. In a specific embodiment, then-type gallium and nitrogen containing cladding material issubstantially free from an aluminum species, which leads toimperfections, defects, and other limitations. The device also has anactive region including multiple quantum well structures overlying then-type gallium and nitrogen containing cladding material. In one or morepreferred embodiments, the device also has thin barrier layersconfigured with the multiple well structures. The device has a p-typegallium and nitrogen containing cladding material overlying the activeregion. In a preferred embodiment, the p-type gallium and nitrogencontaining cladding material is substantially free from an aluminumspecies. The device preferably includes a laser stripe region configuredfrom at least the active region and characterized by a cavityorientation substantially parallel to a projection in a c-direction. Thelaser strip region has a first end and a second end. The device also hasa first etched or etched facet provided on the first end of the laserstripe region and a second etched or etched facet provided on the secondend of the laser stripe region. Depending upon the embodiment, thefacets may be etched, etched, or a combination of cleaved and etched. Inyet other embodiments, the present device includes a gallium andnitrogen containing electron blocking region that is substantially freefrom aluminum species. In yet other embodiments, the device does notinclude any electron blocking layer or yet in other embodiments, thereis no aluminum in the cladding layers and/or electron blocking layer,although other embodiments include aluminum containing blocking layers.In still other embodiments, the optical device and method are free fromany aluminum material, which leads to defects, imperfections, and thelike. Further details of these limitations can be found throughout thepresent specification and more particularly below.

In preferred embodiments, the present method and structure issubstantially free from InAlGaN or aluminum bearing species in thecladding layers as conventional techniques, such as those in Yoshizumiet al., “Continuous-Wave operation of 520 nm Green InGaN-Based LaserDiodes on Semi-Polar {20-21} GaN Substrates,” Applied Physics Express 2(2009) 092101. That is, the present laser structure and method aresubstantially free from any aluminum species in the cladding region.Aluminum is generally detrimental. Aluminum often leads to introductionof oxygen in the reactor, which can act as non radiative recombinationcenters to reduce the radiative efficiency and introduce otherlimitations. We also determined that oxygen can compensate p-typedopants in the p-cladding to cause additional resistivity in the opticaldevice. In other aspects, we also determined that aluminum isdetrimental to the MOCVD reactor and can react or pre-react with othergrowth precursors. Use of aluminum cladding layers is also cumbersomeand can take additional time to grow. Accordingly, it is believed thatthe aluminum cladding free laser method and structure are generally moreefficient to grow than conventional laser structures. Further benefitsare described throughout the present specification and more particularlybelow.

In alternative example, the present invention provides a green laserdiode configured using a semipolar gallium and nitrogen containing bulksubstrate member, as described in more detail below, which has etchedfacets.

In preferred embodiments, the invention provides a laser structurewithout an aluminum bearing cladding region. In a specific embodiment,the laser device comprises a multi-quantum well active region havingthin barrier layers, with the active region comprising three or morequantum well structures. Between each of the quantum well structures isa thin barrier layer, e.g., 8 nm and less, 7 nm and less, 6 nm and less,5 nm and less, 4 nm and less, 3 nm and less, 2 nm and less, 1.5 nm andless. In a preferred embodiment, the combination of thin barrier layersconfigured in the multi-quantum well structures enables a low voltage(e.g., 7 volts and less, 6 volts and less) laser diode free from use ofaluminum bearing cladding regions.

In one embodiment, the optical device has a gallium and nitrogencontaining substrate including a {20-21} crystalline surface regionorientation, which may be off-cut. The device preferably has an n-typecladding material overlying the n-type gallium and nitrogen containingmaterial according to a specific embodiment. The n-type claddingmaterial is substantially free from an aluminum bearing material. Thedevice also has an active region comprising at least three quantumwells. Each of the quantum wells has a thickness of 2.5 nm and greateror 3.5 nm and greater and one or more barrier layers. Each of thebarrier layers has a thickness ranging from about 2 nm to about 4 nm orabout 3 nm to about 6.5 nm and is configured between a pair of quantumwells according to a specific embodiment. At least one or each of thebarrier layers has a thickness ranging from about 2 nm to about 4 nm andis configured between a pair of quantum wells or adjacent to a quantumwell according to a specific embodiment. At least one or each of thebarrier layers has a thickness ranging from about 3 nm to about 6.5 nmand is configured between a pair of quantum wells or adjacent to aquantum well according to a specific embodiment. Preferably, the devicehas a p-type cladding material overlying the active region. Preferably,the p-type cladding material is substantially free from an aluminumbearing material according to a specific embodiment. In a preferredembodiment, the active region is configured operably for a forwardvoltage of less than about 7V or less than about 6V for the device foran output power of 60 mW and greater.

In yet an alternative embodiment, the present invention provides anoptical device. The device has a gallium and nitrogen containingsubstrate including a {20-21} crystalline surface region orientation.The device also has an n-type cladding material overlying the n-typegallium and nitrogen containing material. The n-type cladding materialis substantially free from an aluminum bearing material. The devicefurther has an active region comprising at least two quantum wells. Eachof the quantum wells has a thickness of 2.5 nm and greater or 3.5 nm andgreater and one or more barrier layers according to a specificembodiment. Each of the barrier layers has a thickness ranging fromabout 2 nm to about 5 nm or about 3 nm to about 8 nm according to aspecific embodiment. Each of the barrier layers is configured between apair of quantum wells according to one or more embodiments. At least oneor each of the barrier layers has a thickness ranging from about 2 nm toabout 5 nm and is configured between a pair of quantum wells or adjacentto a quantum well according to a specific embodiment. At least one oreach of the barrier layers has a thickness ranging from about 3 nm toabout 8 nm and is configured between a pair of quantum wells or adjacentto a quantum well according to a specific embodiment. The device alsohas a p-type cladding material overlying the active region. The p-typecladding material is substantially free from an aluminum bearingmaterial according to a preferred embodiment. The device optionally hasa p-type material overlying the p-type cladding material.

In other embodiments, the invention provides yet an alternative opticaldevice, which has a gallium and nitrogen containing substrate includinga {20-21} crystalline surface region orientation. An n-type claddingmaterial is overlying the n-type gallium and nitrogen containingmaterial. Preferably, the n-type cladding material is substantially freefrom an aluminum bearing material. The device has an active regioncomprising at least two quantum wells, each of which has a thickness of2.5 nm and greater. The device has one or more barrier layers, each ofwhich has an n-type impurity characteristic and a thickness ranging fromabout 2 nm to about 5 nm or about 3 nm to about 8 nm in one or morealternative embodiments. Preferably, each of the barrier layers isconfigured between a pair of quantum wells according to a specificembodiment. The device also has a p-type cladding material overlying theactive region according to a specific embodiment. The p-type claddingmaterial is substantially free from an aluminum bearing materialaccording to a specific embodiment. The device also has a p-typematerial overlying the p-type cladding material.

In other embodiments, the invention provides a method of fabricating anoptical device, which has a gallium and nitrogen containing substrateincluding a {20-21} crystalline surface region orientation. An n-typecladding material is overlying the n-type gallium and nitrogencontaining material. Preferably, the n-type cladding material issubstantially free from an aluminum bearing material. The methodincludes forming an active region comprising at least two quantum wells,each of which has a thickness of 2.5 nm and greater. The device has oneor more barrier layers, each of which has an n-type impuritycharacteristic and a thickness ranging from about 2 nm to about 5 nm orabout 3 nm to about 8 nm in one or more alternative embodiments.Preferably, each of the barrier layers is configured between a pair ofquantum wells according to a specific embodiment. The method alsoincludes forming a p-type cladding material overlying the active regionaccording to a specific embodiment. The p-type cladding material issubstantially free from an aluminum bearing material according to aspecific embodiment. The method also includes forming a p-type materialoverlying the p-type cladding material.

In a specific embodiment, the present invention provides an opticaldevice, such as a laser diode. The device has a gallium and nitrogencontaining substrate including a {20-21} crystalline surface regionorientation, which may be off-cut according to one or more embodiments.The device has an n-type cladding material overlying the n-type galliumand nitrogen containing material. In a preferred embodiment, the n-typecladding material is substantially free from an aluminum bearingmaterial. The device also has an active region comprising at least twoquantum wells. In a specific embodiment, each of the quantum wells has athickness of 2.5 nm and greater and one or more barrier layers accordingto a specific embodiment. Each of the barrier layers has a p-typecharacteristic and a thickness ranging from about 2 nm to about 3.5 nmin a specific embodiment. Each of the barrier layers has a p-typecharacteristic and a thickness ranging from about 3.5 nm to about 7 nmin an alternative specific embodiment. In a preferred embodiment, eachof the barrier layers is configured between a pair of quantum wells. Thedevice also has a p-type cladding material overlying the active region.Preferably, the p-type cladding material is substantially free from analuminum bearing material. And overlying p-type material is included. Ina preferred embodiment, the active region is configured for a forwardvoltage of less than about 6v or less than about 7V for the device foran output power of 60 mW and greater.

In one or more embodiments, the present invention includes a laser diodesubstantially free from an aluminum containing cladding region. To formthe laser diode without an aluminum containing cladding region, thepresent laser diode includes three or more quantum wells to provideenough confinement of the optical mode for sufficient gain to reachlasing. However, when the number of quantum wells increases in theactive region, the forward voltage of the diode can increase, as atradeoff. We have determined that the forward voltage of the diode canbe reduced in multi-quantum well active regions by way of the use ofthin barriers on the order of 5 nm, which are much thinner thanconventional lasers such as those in Yoshizumi et al., “Continuous-Waveoperation of 520 nm Green InGaN-Based Laser Diodes on Semi-Polar {20-21}GaN Substrates,” Applied Physics Express 2 (2009) 092101. We have alsodetermined that the forward voltage can be reduced in multi-quantum wellactive regions by adding p or n-type dopant species to the active regionaccording to one or more other embodiments. Although any one orcombination of these approached can be used, we believe it would bepreferable to use the thin barrier approach to avoid adding impuritiesto the active region. The impurities may change optical losses and alterthe electrical junction placement according to one or more embodiments.Accordingly, the present invention provides a laser device and methodthat is free from aluminum-containing cladding regions with low voltageon {20-21) substrates.

Moreover, the present invention provides an optical device that issubstantially free from aluminum bearing cladding materials. The devicehas a gallium and nitrogen containing substrate member having a {20-21}crystalline surface region. The device has an n-type gallium andnitrogen containing cladding material. In a specific embodiment, then-type gallium and nitrogen containing cladding material issubstantially free from an aluminum species, which leads toimperfections, defects, and other limitations. The device also has anactive region including multiple quantum well structures overlying then-type gallium and nitrogen containing cladding material. In one or morepreferred embodiments, the device also has thin barrier layersconfigured with the multiple well structures. The device has a p-typegallium and nitrogen containing cladding material overlying the activeregion. In a preferred embodiment, the p-type gallium and nitrogencontaining cladding material is substantially free from an aluminumspecies. The device preferably includes a laser stripe region configuredfrom at least the active region and characterized by a cavityorientation substantially parallel to a projection in a c-direction. Thelaser strip region has a first end and a second end. The device also hasa first etched facet provided on the first end of the laser striperegion and a second etched facet provided on the second end of the laserstripe region. In yet other embodiments, the present device includes agallium and nitrogen containing electron blocking region that issubstantially free from aluminum species. In yet other embodiments, thedevice does not include any electron blocking layer or yet in otherembodiments, there is no aluminum in the cladding layers and/or electronblocking layer, although other embodiments include aluminum containingblocking layers. In still other embodiments, the optical device andmethod are free from any aluminum material, which leads to defects,imperfections, and the like.

In preferred embodiments, the present method and structure issubstantially free from InAlGaN or aluminum bearing species in thecladding layers as conventional techniques, such as those in Yoshizumiet al., “Continuous-Wave operation of 520 nm Green InGaN-Based LaserDiodes on Semi-Polar {20-21} GaN Substrates,” Applied Physics Express 2(2009) 092101. That is, the present laser structure and method aresubstantially free from any aluminum species in the cladding region.Aluminum is generally detrimental. Aluminum often leads to introductionof oxygen in the reactor, which can act as non radiative recombinationcenters to reduce the radiative efficiency and introduce otherlimitations. We also determined that oxygen can compensate p-typedopants in the p-cladding to cause additional resistivity in the opticaldevice. In other aspects, we also determined that aluminum isdetrimental to the MOCVD reactor and can react or pre-react with othergrowth precursors. Use of aluminum cladding layers is also cumbersomeand can take additional time to grow. Accordingly, it is believed thatthe aluminum cladding free laser method and structure are generally moreefficient to grow than conventional laser structures.

In a specific embodiment on the {20-21} GaN, the device has a laserstripe region formed overlying a portion of the off-cut crystallineorientation surface region. In a specific embodiment, the laser striperegion is characterized by a cavity orientation substantially in aprojection of a c-direction, which is substantially normal to ana-direction. In a specific embodiment, the laser strip region has afirst end and a second end, each of which is etched. In a preferredembodiment, the device is formed on a projection of a c-direction on a{20-21} gallium and nitrogen containing substrate having a pair ofetched mirror structures, which face each other.

In a preferred embodiment, the device has a first etched facet providedon the first end of the laser stripe region and a second etched facetprovided on the second end of the laser stripe region. In one or moreembodiments, the first etched is substantially parallel with the secondetched facet. Mirror surfaces are formed on each of the etched surfaces.The first etched facet comprises a first mirror surface. In a specificembodiment, the first mirror surface comprises a reflective coating. Thereflective coating is selected from silicon dioxide, hafnia, andtitania, tantalum pentoxide, zirconia, including combinations, and thelike. Depending upon the embodiment, the first mirror surface can alsocomprise an anti-reflective coating.

Also in a preferred embodiment, the second etched facet comprises asecond mirror surface. In a specific embodiment, the second mirrorsurface comprises a reflective coating, such as silicon dioxide, hafnia,and titania, tantalum pentoxide, zirconia, combinations, and the like.In a specific embodiment, the second mirror surface comprises ananti-reflective coating.

In a specific embodiment, the laser stripe has a length and width. Thelength ranges from about 50 microns to about 3000 microns or preferablyfrom about 400 microns to about 650 microns or about 650 microns toabout 1200 microns. The strip also has a width ranging from about 0.5microns to about 50 microns or preferably between 1 microns to about 1.5microns, about 1.5 microns to about 2.0 microns, or about 2.0 microns toabout 4 microns, but can be other dimensions. In a specific embodiment,the width is substantially constant in dimension, although there may beslight variations. The width and length are often formed using a maskingand etching process, which are commonly used in the art.

In a specific embodiment, the present invention provides an alternativedevice structure capable of emitting 501 nm and greater light in a ridgelaser embodiment having etched facets. The device is provided with oneor more of the following epitaxially grown elements, but is notlimiting.

-   -   an n-GaN cladding layer with a thickness from 100 nm to 3000 nm        with Si doping level of 5E17 cm⁻³ to 3E18 cm⁻³;    -   an n-side SCH layer comprised of InGaN with molar fraction of        indium of between 3% and 10% and thickness from 20 nm to 150 nm;    -   multiple quantum well active region layers comprised of at least        two 2.0 nm to 5.5 nm InGaN quantum wells separated by thin 2.5        nm and greater, and optionally up to about 8 nm, GaN barriers;    -   a barrier region formed overlying the active region;    -   a p-side SCH layer comprised of InGaN with molar a fraction of        indium of between 1% and 10% and a thickness from 15 nm to 100        nm;    -   an electron blocking layer comprised of AlGaN with molar        fraction of aluminum of between 5% and 20% and thickness from 5        nm to 20 nm and doped with Mg;    -   a p-GaN cladding layer with a thickness from 400 nm to 1000 nm        with Mg doping level of 2E17 cm⁻³ to 2E19 cm⁻³; and    -   a p++-GaN contact layer with a thickness from 20 nm to 40 nm        with Mg doping level of 1E19 cm⁻³ to 1E21 cm⁻³.

Of course there can be other embodiments such as the use of p-side GaNguiding layer in place of the p-SCH, the use of multiple differentlayers in the SCH regions, or the omission of the EBL layer.

In an example, a laser device is fabricated on a {20-21} substrateaccording to an embodiment of the present invention. The laser deviceincludes gallium nitride substrate, which has an underlying n-type metalback contact region. In a specific embodiment, the metal back contactregion is made of a suitable material such as those noted below andothers. Further details of the contact region can be found throughoutthe present specification, and more particularly below.

In a specific embodiment, the device also has an overlying n-typegallium nitride layer, an active region, and an overlying p-type galliumnitride layer structured as a laser stripe region. In a specificembodiment, each of these regions is formed using at least an epitaxialdeposition technique of metal organic chemical vapor deposition (MOCVD),molecular beam epitaxy (MBE), or other epitaxial growth techniquessuitable for GaN growth. In a specific embodiment, the epitaxial layeris a high quality epitaxial layer overlying the n-type gallium nitridelayer. In some embodiments the high quality layer is doped, for example,with Si or O to form n-type material, with a dopant concentrationbetween about 10¹⁶ cm⁻³ and 10²⁰ cm⁻³.

In a specific embodiment, an n-type Al_(u)In_(v)Ga_(1-u-v)N layer, where0≦u, v, u+v≦1, is deposited on the substrate. In a specific embodiment,the carrier concentration may lie in the range between about 10¹⁶ cm⁻³and 10²⁰ cm⁻³. The deposition may be performed using metalorganicchemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).

As an example, the bulk GaN substrate is placed on a susceptor in anMOCVD reactor. After closing, evacuating, and back-filling the reactor(or using a load lock configuration) to atmospheric pressure, thesusceptor is heated to a temperature between about 1000 and about 1200degrees Celsius in the presence of a nitrogen-containing gas. In onespecific embodiment, the susceptor is heated to approximately 900 to1100 degrees Celsius under flowing ammonia. A flow of agallium-containing metalorganic precursor, such as trimethylgallium(TMG) or triethylgallium (TEG) is initiated, in a carrier gas, at atotal rate between approximately 1 and 50 standard cubic centimeters perminute (sccm). The carrier gas may comprise hydrogen, helium, nitrogen,or argon. The ratio of the flow rate of the group V precursor (ammonia)to that of the group III precursor (trimethylgallium, triethylgallium,trimethylindium, trimethylaluminum) during growth is between about 2000and about 12000. A flow of disilane in a carrier gas, with a total flowrate of between about 0.1 sccm and 10 sccm, is initiated.

In a specific embodiment, the laser stripe region is made of the p-typegallium nitride layer. In a specific embodiment, the laser stripe isprovided by an etching process selected from dry etching or wet etching.In a preferred embodiment, the etching process is dry, but can beothers. As an example, the dry etching process is an inductively coupledprocess using chlorine bearing species or a reactive ion etching processusing similar chemistries. Again as an example, the chlorine bearingspecies are commonly derived from chlorine gas or the like. The devicealso has an overlying dielectric region, which exposes contact region.In a specific embodiment, the dielectric region is an oxide such assilicon dioxide or silicon nitride, but can be others. The contactregion is coupled to an overlying metal layer. The overlying metal layeris a multilayered structure containing gold and platinum (Pt/Au), nickelgold (Ni/Au), but can be others.

In a specific embodiment, the laser device has active region. The activeregion can include one to twenty quantum well regions according to oneor more embodiments. As an example following deposition of the n-typeAl_(u)In_(v)Ga_(1-u-v)N layer for a predetermined period of time, so asto achieve a predetermined thickness, an active layer is deposited. Theactive layer may be comprised of multiple quantum wells, with 2-10quantum wells. The quantum wells may be comprised of InGaN with GaNbarrier layers separating them. In other embodiments, the well layersand barrier layers comprise Al_(w)In_(x)Ga_(1-w-x)N andAl_(y)In_(z)Ga_(1-y-z)N, respectively, where 0≦w, x, y, z, w+x, y+z≦1,where w<u, y and/or x>v, z so that the bandgap of the well layer(s) isless than that of the barrier layer(s) and the n-type layer. The welllayers and barrier layers may each have a thickness between about 1 nmand about 20 nm. The composition and structure of the active layer arechosen to provide light emission at a preselected wavelength. The activelayer may be left undoped (or unintentionally doped) or may be dopedn-type or p-type.

In a specific embodiment, the active region can also include an electronblocking region, and a separate confinement heterostructure. In someembodiments, an electron blocking layer is preferably deposited. Theelectron-blocking layer may comprise Al_(s)In_(1-s-t)N, where 0≦s, t,s+t≦1, with a higher bandgap than the active layer, and may be dopedp-type. In one specific embodiment, the electron blocking layercomprises AlGaN. In another embodiment, the electron blocking layercomprises an AlGaN/GaN super-lattice structure, comprising alternatinglayers of AlGaN and GaN, each with a thickness between about 0.2 nm andabout 5 nm.

In a specific embodiment, the action region structure does not includean AlGaN EBL layer. That is, the laser device is free from any electronblocking layer, which is optional in such embodiment.

As noted, the p-type gallium nitride structure is deposited above theelectron blocking layer and active layer(s). The p-type layer may bedoped with Mg, to a level between about 10¹⁶ cm⁻³ and 10²² cm⁻³, and mayhave a thickness between about 5 nm and about 1000 nm. The outermost1-50 nm of the p-type layer may be doped more heavily than the rest ofthe layer, so as to enable an improved electrical contact. In a specificembodiment, the laser stripe is provided by an etching process selectedfrom dry etching or wet etching. In a preferred embodiment, the etchingprocess is dry, but can be others. The device also has an overlyingdielectric region, which exposes a contact region. In a specificembodiment, the dielectric region is an oxide such as silicon dioxide.

In a specific embodiment, the metal contact is made of suitablematerial. The reflective electrical contact may comprise at least one ofsilver, gold, aluminum, nickel, platinum, rhodium, palladium, chromium,or the like. The electrical contact may be deposited by thermalevaporation, electron beam evaporation, electroplating, sputtering, oranother suitable technique. In a preferred embodiment, the electricalcontact serves as a p-type electrode for the optical device. In anotherembodiment, the electrical contact serves as an n-type electrode for theoptical device.

In an example, a laser device includes a starting material such as abulk nonpolar or semipolar GaN substrate, but can be others. In aspecific embodiment, the device is configured to achieve emissionwavelength ranges of 390 nm to 420 nm, 420 nm to 440 nm, 440 nm to 470nm, 470 nm to 490 nm, 490 nm to 510 nm, and 510 nm to 530 nm, but can beothers.

In a preferred embodiment, the growth structure is configured usingbetween 3 and 5 or 5 and 7 quantum wells positioned between n-type GaNand p-type GaN cladding layers. In a specific embodiment, the n-type GaNcladding layer ranges in thickness from 500 nm to 2000 nm and has ann-type dopant such as Si with a doping level of between 1E18 cm⁻³ and3E18 cm⁻³. In a specific embodiment, the p-type GaN cladding layerranges in thickness from 500 nm to 1000 nm and has a p-type dopant suchas Mg with a doping level of between 1E17 cm⁻³ and 7E19 cm⁻³. In aspecific embodiment, the Mg doping level is graded such that theconcentration would be lower in the region closer to the quantum wells.

In a specific preferred embodiment, the quantum wells have a thicknessof between 2.5 nm and 4 nm, 4 nm and 5.5 nm or 5.5 nm and 8 nm, but canbe others. In a specific embodiment, the quantum wells would beseparated by barrier layers with thicknesses between 2 nm and 3.5 nm or3.5 nm and 6 nm or 6 nm and 8 nm. The quantum wells and the barrierstogether comprise a multiple quantum well (MQW) region.

In a preferred embodiment, the device has barrier layers formed fromGaN, InGaN, AlGaN, or InAlGaN. In a specific embodiment using InGaNbarriers, the indium contents range from 0% to 5% (mole percent), butcan be others. Also, it should be noted that % of indium or aluminum isin a molar fraction, not weight percent.

An InGaN separate confinement heterostructure layer (SCH) could bepositioned between the n-type GaN cladding and the MQW region accordingto one or more embodiments. Typically, such separate confinement layeris commonly called the n-side SCH. The n-side SCH layer ranges inthickness from 10 nm to 60 nm or 60 nm to 150 nm and ranges in indiumcomposition from 1% to 12% (mole percent), but can be others. In aspecific embodiment, the n-side SCH layer may be doped with an n-typedopant such as Si.

In yet another preferred embodiment, an InGaN separate confinementheterostructure layer (SCH) is positioned between the p-type GaNcladding and the MQW region, which is called the p-side SCH. In aspecific embodiment, the p-side SCH layer ranges in thickness from 10 nmto 40 nm or 40 nm to 150 nm and ranges in indium composition from 0% to10% (mole percent), but can be others. The p-side SCH layer may be dopedwith a p-type dopant such as Mg.

In another embodiment, the structure would contain both an n-side SCHand a p-side SCH. In another embodiment the p-side SCH would be replacedwith p-side GaN guiding layer. In another embodiment the n-side and/orp-side SCH regions would contain multiple layers.

In another embodiment, the structure would contain a GaN guiding layeron the p-side positioned between the p-type GaN cladding layer and theMQW region. This GaN guiding layer could range in thickness from 10 nmto 60 nm and may or may not be doped with a p-type species such as Mg.

In a specific preferred embodiment, an AlGaN electron blocking layer,with an aluminum content of between 5% and 20% (mole percent), ispositioned between the MQW and the p-type GaN cladding layer eitherbetween the MQW and the p-side SCH, within the p-side SCH, or betweenthe p-side SCH and the p-type GaN cladding. The AlGaN electron blockinglayer ranges in thickness from 5 nm to 20 nm and is doped with a p-typedopant such as Mg from 1E17 cm⁻³ and 1E21 cm⁻³ according to a specificembodiment. In other embodiments, the electron blocking layer is freefrom any aluminum species and/or may be eliminated altogether. In yetanother embodiment, the device would be substantially free from anelectron blocking layer.

Preferably, a p-contact layer positioned on top of and is formedoverlying the p-type cladding layer. The p-contact layer would becomprised of GaN doped with a p-dopant such as Mg at a level rangingfrom 1E20 cm⁻³ to 1E22 cm⁻³.

In an example, a laser device has a gallium and nitrogen containingsubstrate member (e.g., bulk gallium nitride) having a {20-21}crystalline surface region or other surface configuration. The devicehas an n-type gallium and nitrogen containing cladding material. In aspecific embodiment, the n-type gallium and nitrogen containing claddingmaterial is substantially free from an aluminum species, which leads toimperfections, impurities, and other limitations. In one or morepreferred embodiment, the cladding material has no aluminum species andis made of a gallium and nitrogen containing material.

In a specific embodiment, the device also has an active region includingmultiple quantum well structures overlying the n-type gallium andnitrogen containing cladding material. In one or more embodiments, theactive regions can include those noted, as well as others. That is, thedevice can include InGaN/InGaN and/or InGaN/GaN active regions, amongothers. In a specific embodiment, the optical can include seven MQW, sixMQW, five MQW, four MQW, three MQW, more MQW, or fewer, and the like.

In a specific embodiment, the device has a p-type gallium and nitrogencontaining cladding material overlying the active region. In a preferredembodiment, the p-type gallium and nitrogen containing cladding materialis substantially free from an aluminum species, which leads toimperfections, defects, and other limitations. In one or more preferredembodiment, the cladding material has no aluminum species and is made ofa gallium and nitrogen containing material.

In a specific embodiment, the device preferably includes a laser striperegion configured from at least the active region and characterized by acavity orientation substantially parallel to a projection in ac-direction. Other configurations may also exist depending upon thespecific embodiment. The laser strip region has a first end and a secondend or other configurations. In a specific embodiment, the device alsohas a first etched facet provided on the first end of the laser striperegion and a second etched facet provided on the second end of the laserstripe region.

In yet other embodiments, the present device includes a gallium andnitrogen containing electron blocking region that is substantially freefrom aluminum species. In yet other embodiments, the device does notinclude any electron blocking layer or yet in other embodiments, thereis no aluminum in the cladding layers and/or electron blocking layer.

In preferred embodiments, the present method and structure issubstantially free from InAlGaN or aluminum bearing species in thecladding layers as conventional techniques, such as those in Yoshizumiet al., “Continuous-Wave operation of 520 nm Green InGaN-Based LaserDiodes on Semi-Polar {20-21} GaN Substrates,” Applied Physics Express 2(2009) 092101. That is, the present laser structure and method aresubstantially free from any aluminum species in the cladding region.Aluminum is generally detrimental. Aluminum often leads to introductionof oxygen in the reactor, which can act as non radiative recombinationcenters to reduce the radiative efficiency and introduce otherlimitations. We also determined that oxygen can compensate p-typedopants in the p-cladding to cause additional resistivity in the opticaldevice. In other aspects, we also determined that aluminum isdetrimental to the MOCVD reactor and can react or pre-react with othergrowth precursors. Use of aluminum cladding layers is also cumbersomeand can take additional time to grow. Accordingly, it is believed thatthe aluminum cladding free laser method and structure are generally moreefficient to grow than conventional laser structures. Further details ofthe present laser configured on {20-21} can be found in U.S. ApplicationPublication No. 2011/0064101, which is incorporated by reference herein.

In an example, a gallium and nitrogen containing laser device configuredon either a nonpolar or a semipolar surface orientation. The device hasa gallium and nitrogen containing substrate member and a cladding regionoverlying the substrate member. In an example, the device has a cavityregion formed overlying the cladding region and configured in alignmentin substantially a c-direction or a projection of the c-direction.Preferably, a cavity region is characterized by a first end and a secondend. In an example, the device has a first optical coating formedoverlying the first facet, wherein the first coating overlying the firstfacet is configured to increase a reflectivity and a second opticalcoating formed overlying the second facet, wherein the second coatinglayer overlying the second facet is configured to reduce a reflectivity.The device has an optical power density characterizing the laser device,the laser device being substantially free from COMD related failure.

In an example, the nonpolar or semipolar surface orientation comprisesan m-plane, a (30-31) plane, a (20-21) plane, a (30-32) plane, a(30-3-1) plane, a (20-2-1) plane, a (30-3-2) plane, or an offcut ofwithin +/−5 degrees of any of these planes toward an a-direction or ac-direction; the cladding region being substantially free fromAl-containing material, the cladding region being characterized by anAlN mol fraction in the cladding region of less than about 2%. In anexample, the first optical coating is provided by a method selected fromelectron-beam deposition, thermal evaporation, PECVD, sputtering, and acombination of any of the foregoing. In other examples, the presentinvention also includes related methods reciting the same or similarelements.

In an example, the device comprises an output cavity width of greaterthan about 3 μm and less than about 25 μm, and is operable at over 1W orwherein the device comprises an output cavity width of greater thanabout 3 μm and less than about 25 μm and is operable at over 2W orwherein the device comprises an output cavity width of greater thanabout 3 μm and less than about 35 μm, and is operable at over 3W orwherein the device comprises an output cavity width of greater thanabout 3 μm and less than about 35 μm, and is operable at over 4.5W orwherein the device comprises an output cavity width of greater thanabout 3 μm and less than about 50 μm and is operable at over 3W. In anexample, the device is substantially free from COMD for power levelsgreater than 100 mW per micron of output cavity width, 200 mW per micronof output cavity width, or 400 mW per micron of output cavity width.

Finally, it should be noted that there are alternative ways ofimplementing the embodiments disclosed herein. Accordingly, the presentembodiments are to be considered as illustrative and not restrictive.Furthermore, the claims are not to be limited to the details givenherein, and are entitled their full scope and equivalents thereof.

As used herein, the term GaN substrate is associated with GroupIII-nitride based materials including GaN, InGaN, AlGaN, or other GroupIII containing alloys or compositions that are used as startingmaterials. Such starting materials include polar GaN substrates (i.e.,substrate where the largest area surface is nominally an (h k l) planewherein h=k=0, and l is non-zero), non-polar GaN substrates (i.e.,substrate material where the largest area surface is oriented at anangle ranging from about 80-100 degrees from the polar orientationdescribed above toward an (h k l) plane wherein l=0, and at least one ofh and k is non-zero) or semi-polar GaN substrates (i.e., substratematerial where the largest area surface is oriented at an angle rangingfrom about +0.1 to 80 degrees or 110-179.9 degrees from the polarorientation described above toward an (h k l) plane wherein l=0, and atleast one of h and k is non-zero).

As shown, the present device can be enclosed in a suitable package. Suchpackage can include those such as in TO-38 and TO-56 headers. Othersuitable package designs and methods can also exist, such as TO-9 orflat packs where fiber optic coupling is required and even non-standardpackaging. In a specific embodiment, the present device can beimplemented in a co-packaging configuration such as those described inU.S. Pat. No. 8,427,590, which is incorporated by reference in itsentirety.

In other embodiments, the present laser device can be configured in avariety of applications. Such applications include laser displays,metrology, communications, health care and surgery, informationtechnology, and others. As an example, the present laser device can beprovided in a laser display such as those described in U.S. applicationSer. No. 12/789,303 filed on May 27, 2010, which is incorporated byreference in its entirety.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. As an example, the packaged device can include any combination ofelements described above, as well as outside of the presentspecification. As used herein, the term “substrate” can mean the bulksubstrate or can include overlying growth structures such as a galliumand nitrogen containing epitaxial region, or functional regions such asn-type GaN, combinations, and the like. Additionally, the examplesillustrates two waveguide structures in normal configurations, there canbe variations, e.g., other angles and polarizations. For semi-polar, thepresent method and structure includes a stripe oriented perpendicular tothe c-axis, an in-plane polarized mode is not an Eigen-mode of thewaveguide. The polarization rotates to elliptic (if the crystal angle isnot exactly 45 degrees, in that special case the polarization wouldrotate but be linear, like in a half-wave plate). The polarization willof course not rotate toward the propagation direction, which has nointeraction with the Al band. The length of the a-axis stripe determineswhich polarization comes out at the next mirror. In other embodiments,cleaved facets can be configured on the laser stripe. The cleaved facetscan be made by scribe and break or a skip scribing process, althoughthere can be variations.

Although the embodiments above have been described in terms of a laserdiode, the methods and device structures can also be applied to anylight emitting diode device. Therefore, the above description andillustrations should not be taken as limiting the scope of the presentinvention which is defined by the appended claims.

What is claimed is:
 1. A gallium and nitrogen containing laser diodedevice, the device comprising: a gallium and nitrogen containingsubstrate material comprising a surface region, the surface region beingconfigured on either a non-polar {10-10} crystal orientation or asemi-polar {10-10} crystal orientation configured with an offcut at anangle toward or away from the direction; a GaN region formed overlyingthe surface region; an active region formed overlying the surfaceregion; a gettering region comprising a magnesium species overlying thesurface region; and a p-type cladding region comprising an (InAl)GaNmaterial doped with a plurality of magnesium species formed overlyingthe active region.
 2. The device of claim 1, where the semipolar planeis selected from one of a {30-3-1} plane, a {30-31} plane, a{20-2-1}plane, a {20-21} plane, a {30-3-1} plane, a {30-32} plane, or an offcutfrom any one of these planes within +/−5 degrees toward an a-plane or ac-plane.
 3. The device of claim 1, further comprising an electronblocking region between the gettering region and the p-type claddingregion.
 4. The device of claim 1, further comprising a barrier regionbetween the active region and the gettering region.
 5. The device ofclaim 4, wherein the barrier region comprises a layer selected from aGaN layer, an InGaN layer, and a combination thereof.
 6. The device ofclaim 1, further comprising a separate confinement heterostructureregion between the active region and the gettering region, wherein theseparate confinement heterostructure region is configured to confine anoptical mode; the separate confinement heterostructure comprising InGaN.7. The device of claim 6, wherein the separate confinementheterostructure region comprising an InGaN layer.
 8. The device of claim1, wherein the p-type cladding region comprises a plurality of layers,each of the plurality of layers independently selected from a GaN layer,an AlGaN layer, and an InAlGaN layer, where in each of the plurality oflayers is independently doped with a concentration of magnesium.
 9. Thedevice of claim 8, wherein the concentration of magnesium ranges from5E17 cm⁻³ to 3E19 cm⁻³.
 10. The device of claim 1, wherein the getteringregion comprises a magnesium species doped to increase incorporation ofunintentionally incorporated magnesium from a first concentration to asecond concentration.
 11. The device of claim 3, wherein the electronblocking region comprises a material selected from AlGaN and InAlGaN,wherein the material is characterized by an AlN mole fraction rangingfrom 5% to 35%.
 12. The device of claim 3, wherein the electron blockingregion comprises a material selected form AlGaN and AlInGaN; and isconfigured with a wider band gap than a barrier region configured withina vicinity of the electron blocking region.
 13. The device of claim 1,wherein the active region comprises InGaN quantum wells configured toemit in a blue 430 nm-480 nm wavelength range or in a green 500 nm-540nm wavelength range.
 14. The device of claim 1, wherein the activeregion comprises a plurality of quantum well regions.
 15. The device ofclaim 1, wherein the p-type cladding region comprises a single layer.16. The device of claim 1, wherein the p-type region comprises multipleregions.
 17. The device of claim 1, wherein the active region comprisesone or more light emitting layers, each of the one or more lightingemitting layers being configured between a pair of barrier regions, eachof the one or more lighting emitting layers having a thickness rangingfrom 2 nm to about 8 nm; and wherein each of the one or more barrierregions has a thickness ranging from 2 nm to 20 nm or from 2 nm to 4 nmor 4 to 20 nm.
 18. The device of claim 1, further comprising a GaNbarrier region and wherein the p-type cladding region is a GaNp-cladding region substantially free from an aluminum bearing species.19. The device of claim 3, wherein the electron blocking region is dopedwith a magnesium concentration between 5E18 cm⁻³ and 5E19 cm⁻³.
 20. Thedevice of claim 1, wherein the p-type cladding region is a GaNp-cladding doped with a Mg concentration of less than 2E19 cm⁻³ or lessthan about 5E18 cm⁻³.
 21. The device of claim 3, wherein the electronblocking region and the p-type cladding region are epitaxially grown ata temperature above about 900° C.
 22. The device of claim 1, wherein theelectron blocking region and at least a portion of the p-type claddingregion are epitaxially grown at a temperature above about 900° C. andthe gettering region is provided at a temperature of less than about850° C.
 23. The device of claim 1, wherein at least a portion of thep-type cladding region is epitaxially grown at a temperature above about900° C. and the gettering region is provided at a temperature of lessthan about 900° C.
 24. The device of claim 1, wherein at least a portionof the p-type cladding region is epitaxially grown at a temperatureabove about 900° C. and the gettering region is provided at atemperature of less than about 850° C.
 25. The device of claim 1,wherein at least a portion of the p-type cladding region is epitaxiallygrown at a temperature above about 950° C. and the gettering region isprovided at a temperature of less than about 850° C.
 26. The device ofclaim 1, wherein at least a portion of the p-type cladding region isepitaxially grown at a temperature above 1,000° C. and the getteringregion is provided at a temperature of less than about 850° C.
 27. Thedevice of claim 3, wherein the electron blocking region is substantiallyfree from magnesium doping.
 28. The device of claim 1, wherein thegettering region comprises: a region intentionally doped with Mg; and aregion unintentionally doped with Mg region wherein the unintentionallydoped region is configured to incorporate residual Mg before formationof the p-type region.
 29. The device of claim 1, wherein the getteringregion is characterized by a thickness from 2 nm to 50 nm.
 30. Thedevice of claim 1, wherein the gettering region comprises a materialselected from GaN, AlGaN, InAlGaN, and a combination of any of theforegoing.
 31. The device of claim 3, wherein the electron blockingregion comprises a material selected from GaN, InAlN, AlInGaN, and acombination of any of the foregoing.
 32. A method for manufacturing agallium and nitrogen containing laser diode device, the methodcomprising: providing a gallium and nitrogen containing substratematerial comprising a surface region, the surface region beingconfigured on either a non-polar {10-10} crystal orientation or asemi-polar {10-10} crystal orientation configured with an offcut at anangle toward or away from the [0001] direction; forming a GaN regionoverlying the surface region; forming an active region overlying thesurface region; forming a gettering region comprising a magnesiumspecies overlying the surface region; and forming a p-type claddingregion comprising an (InAl)GaN material doped with a plurality ofmagnesium species overlying the active region.
 33. The method of claim32, wherein the semi-polar plane is selected from a {40-4-1} plane, a{-40-41} plane, a {30-3-1} plane, a {30-31} plane, a {20-2-1} plane, a{20-21} plane, a {30-3-1} plane, a {30-32} plane, or an offcut from anyone of these planes within +/−5 degrees toward an a-plane or a c-plane.34. The method of claim 32, further comprising forming an electronblocking region between the gettering region and the p-type claddingregion.
 35. The method of claim 32, further comprising forming a barrierregion between the active region and the gettering region.
 36. Themethod of claim 35, wherein the barrier region comprises GaN layers,InGaN layers, or a combination thereof.
 37. The method of claim 32,further comprising forming a separate confinement heterostructure regionbetween the active region and the gettering region, wherein the separateconfinement heterostructure configured to confine an optical mode. 38.The method of claim 37, wherein the separate confinement heterostructureregion comprises an InGaN layer.
 39. The method of claim 32, wherein thep-type cladding region comprises a plurality of layers, each of theplurality of layers comprising a material independently selected fromGaN, AlGaN, and InAlGaN, wherein each of the plurality of layers isindependently doped with a concentration of magnesium.
 40. The method ofclaim 39, wherein the concentration of magnesium ranges from 5E17 cm⁻³to 3E19 cm⁻³.
 41. The method of claim 32, wherein the gettering regioncomprises a magnesium species doped to increase incorporation ofunintentionally incorporated magnesium from a first concentration to asecond concentration.
 42. The method of claim 34, wherein the electronblocking region comprises a material selected from AlGaN and InAlGaN,wherein the material is characterized by an AlN mole fraction rangingfrom 5% to 35%.
 43. The method of claim 32, wherein the active regioncomprises InGaN quantum wells configured to emit in a blue 430 nm to 48nm wavelength range or in the green 500 nm to 540 nm wavelength range.44. The method of claim 32, wherein the active region comprises aplurality of quantum well regions.
 45. The method of claim 32, whereinthe p-type cladding region comprises a single layer.
 46. The method ofclaim 32, wherein the p-type region comprises multiple regions.
 47. Themethod of claim 32, wherein the active region comprises one or morelight emitting layers, each of the one or more lighting emitting layersbeing configured between a pair of barrier regions, each of the one ormore lighting emitting layers having a thickness ranging from 2 nm toabout 8 nm; and wherein each of the barrier regions has a thicknessranging from 2 nm to 20 nm or from 2 to 4 nm or 4 to 20 nm.
 48. Themethod of claim 32, further comprising forming a GaN barrier region; andwherein the p-type cladding region is a GaN p-cladding regionsubstantially free from an aluminum bearing species.
 49. The method ofclaim 34, wherein the electron blocking region is doped with a magnesiumconcentration between 5E18 cm⁻³ and 5E19 cm⁻³.
 50. The method of claim36, wherein the p-type region is a GaN p-cladding doped with a Mgconcentration less than 2E19 cm⁻³ or less than about 5E18 cm⁻³.
 51. Themethod of claim 34, wherein the electron blocking region and the p-typecladding region are epitaxially grown at a temperature above about 900C.
 52. The method of claim 32, wherein the electron blocking region andthe p-type cladding region are epitaxially grown at a temperature aboveabout 900° C. and the gettering region is provided at a temperature ofless than about 850° C.
 53. The method of claim 32, wherein at least aportion of the p-type cladding region is epitaxially grown at atemperature above about 900° C. and the gettering region is provided ata temperature of less than about 900° C.
 54. The method of claim 32,wherein at least a portion of the p-type cladding region is epitaxiallygrown at a temperature above about 900° C. and the gettering region isprovided at a temperature of less than 850° C.
 55. The method of claim32, wherein at least a portion of the p-type cladding region isepitaxially grown at a temperature above about 950° C. and the getteringregion is provided at a temperature of less than about 850° C.
 56. Themethod of claim 32, wherein at least a portion of the p-type claddingregion is epitaxially grown at a temperature above about 1,000° C. andthe gettering region is provided at a temperature of less than about850° C.
 57. The method of claim 34, wherein the electron blocking regionis substantially free from magnesium doping.
 58. The method of claim 32,wherein the gettering region comprise: a region intentionally doped withMg; and a region unintentionally doped with Mg, wherein theunintentionally doped region is configured to incorporate residual Mgbefore formation of the p-type region.
 59. The method of claim 32,wherein the gettering region comprises a thickness of 2 nm to 50 nm. 60.The method of claim 32, wherein the gettering region comprises amaterial selected from GaN, AlGaN, InAlGaN, and a combination of any ofthe foregoing.
 61. The method of claim 34, wherein the electron blockingregion comprises a material selected from GaN, InAlN, AlInGaN, and acombination of any of the foregoing.